This invention relates to a secondary air introducing apparatus chiefly in a four-cycle type internal combustion engine for a vehicle.
It has been known to provide a secondary air introducing opening in a side wall of a cylinder of an internal combustion engine with the opening located near the bottom dead center point of a piston mounted in the cylinder. The opening is generally opened and closed by the piston and is connected through an introducing passage with a secondary air supply source comprising an air pump or the like. It has been usual with this type of apparatus that the introducing passage is so formed that at least a part thereof extends radially sideways or downwardly. Accordingly, this produces a problem that fuel or lubrication oil leaked out from the cylinder into the introducing passage through the introducing opening can be stagnated in the passage or introduced therethrough into the supply source, and thereby instable combustion, damage of the supply source or the like is liable to be caused.